Damage to materials due to use and environmental conditions is problematic in many industries. Corrosion, ablation and erosion are examples of material damage that effect industrial applicability and use resulting in increased maintenance costs, compromised safety, higher production costs and other negative results. In order to mitigate this damage, corrosion monitoring is necessary.
In the aeronautical industry, for example, thermal protection systems are critical for the protection of space vehicles and payloads during re-entry. The thermal protection system is usually attached to the entire front surface of the aero-shell that bears the major blunt of atmospheric re-entry. The mission success of the space vehicle is fundamentally dependent on the thermal protection system material protecting the aero-shell from the aggressive conditions encountered during entry. Several entry conditions (e.g. radiation, shock and ionization) combine to ablate the thermal protection system material and their effects increase as the anticipated size and mass of future vehicles destined for planets with atmosphere increases. It is, therefore, important to determine the temperature and rate at which the thermal protection system material recedes toward the aero-shell due to ablation.
The current state of the art of instrumentation of the thermal protection system uses conventional thermocouples and resistors to sense temperature and resistance, respectively. These thermocouples and resistors are manually placed in cylindrical plugs that are made from the temperature protection system material. The plugs are subsequently inserted in holes drilled in the main thermal protection system material that is incorporated into the aero-shell. The purpose of the thermocouples is to measure the temperature spatial and temporal temperature gradient along the trajectory axis of the thermal protection system material and also over the surface of the thermal protection system. The resistor measures the ablation of the char layer of the thermal protections system material. The sensors are embedded in the plug with the thermocouple and then inserted into the main thermal protection system material.
There are several problems with these sensor arrangements. First, these instrumented plugs are time consuming to manufacture and problematic to integrate into a space vehicle. Integration requires machining holes to accommodate these instrumented cylindrical plugs. The cost and time to integrate plugs into a heat shield of the space vehicle can have significant cost and schedule impacts. Presently, insertion and gluing of the plug into the thermal protection system material leaves a circular boundary of homogeneous material discontinuity between the plug and the main thermal protection system. The circular boundary is defined by the glue material. During entry phase, the boundary layer shock/thermal protection system interaction could preferentially ablate this circular boundary section, leading to enhanced turbulence and accelerated ablation. The potential result would be the disgorging of the plug and exposure of the aero-shell, thus compromising the safety of the vehicle. To dramatically reduce the impact of incorporating instrumentation into a thermal protection system of the space vehicle, a new measurement system and methodology is needed.
Second, the plug approach limits the number of thermocouple and resistor carrying plugs that can be positioned in the thermal protection system. Too many plugs, for the purpose of improving area coverage and resolution, could potentially affect the structural and mechanical integrity of the thermal protection system material. It could also increase the number of possible sites for shock induced damage. Also, the manual arrangement of the sensors within the plug severely reduces the number of sensors needed for high resolution profiling of the temperature gradient and the ablation recession rate. Additionally, due to the limited number of sensors, a high resolution, large area tomographic profile of the thermal protection system is impossible to obtain.
It is anticipated that the thermal protection system area will continue to increase with increasing payload, a tomographic profile of the condition of the thermal protection system becomes important in monitoring entry and actively changing the entry axis to avoid risks. Accordingly, to improve thermal protection systems of space vehicles as well as detecting damage to materials of other surfaces, whether caused by corrosion, ablation or the like, a new system and method of use is needed.